Most
are
immotile.
Cell
size
(diameter)
varies
between
0.3-0.9 µm.
Reproduction
is
by
binary
fission.
Based
on
nutritional
requirements,
two
rrincipal
genera
are
recognized,
the
genus
Mycoplasma
which
has
a
specific
requirement
of
sterol
and
cholesterol
and
the
genus
Acholeplasma
which
does
not
require
cholesterol.
Because
of
the
absence
of
cell
wall
they
are
insensitive
to
penicillin.
Colonies
on
solid
media
have
a
fried
egg
like
structure
consisting
of
an
opaque
area
partly
embedded
in
the
substrate
and
a
translucent
periphery.
Measurement
of
genome
size
suggests
Mycoplasma
spp.
to
have
one
half
or
less
of
DNA
than
that
to
other
procaryotes
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